Sequence and welding timer



FIG. I

Dec. 4," 1951 D, P, FAULK 2,577,411

' SEQUENCE AND WELDING TIMER Filed Jan. 31, 1950 7 Sheets-Sheet 1 &

Dec. 4, 1951 D. P. FAULK SEQUENCE AND WELDING TIMER f7 Sheets-Sheet 2Filed Jan. 51, 1950 INVENTOI? DONALD P FAULK BY Z A NEV Dec. 4, 1951 D.P. FAUI ..K

SEQUENCE AND WELDING TIMER '7 Sheefs-Sheet 3 Filed Jan. 51, 1950INVENTOR DONALD P. FAULK AT 0 NEY Dec. 4, 1951 D. P. FAULK 2,577,411

SEQUENCE AND WELDING TIMER Filed Jan. 31, 1950 'I'SheetS-Sheet 4 F i-fififififi fi $3 I I III I g In I I s I i I l I s; i l I Ch I a 3 l N II m (D \g fi I g W I I I I l I I l I I I I Wye/woe DONALD l2 FAULK E BY8L 31M A TTD/ZNEY Dec. 4, 1951 D. P. FAULK SEQUENCE AND WELDING TIMER '7Sheeis-Sheet 6 Filed Jan. 31, 1950 mSth INVENTOI? DONALD P FAULK Dec. 4,1951 D. P. FAULK SEQUENCE AND WELDING TIMER '7 Sheets-Sheet 7 Filed Jan.51, 1950 Sl70/I Si70/1 /NVENTO/? DONALD R FAULK BY w ATTOPNE V PatentedDec. 4, 1951 UNITED STATES PATENT OFFICE SEQUENCE AND WELDING TIlVIERDonald P. Faulk, Lexington, Mass., assignor to Raytheon ManufacturingCompany, Newton, Mass., a corporation of Delaware Application January31, 1950, Serial No. 141,518

25 Claims. (01. 315-246) novel circuit arrangements, has succeeded inachievin these timing functions very accurately with a much smallernumber of control relays and tubes than have heretofore been used forcomparable functions. Such a drastic reduction in tube and relayrequirements has also resulted in similar reductions in necessary wiringand in manufacturing time, thereby materially adding the additionaladvantage of reduced space requirements and manufacturing costs.

In addition to the above advantages, the invention makes use of a novelarrangement for synchronous operation with line voltage and is adaptedfor both synchronous and nonsynchronous operation, and for bothpulsation and spotwelding at speeds substantially higher than heretoforepossible. The embodiments adapted for synchronous operation areinherently full cycling. The embodiments adapted for pulsation weldingautomatically time only an integral number of "heat times.Self-compensatingfeatures in the system insure accuracy in sequence andweld timing despite poor line voltage conditions, temperaturevariations, or dust accumulation.

The invention achieves these advantages by providing generally a cascadearrangement of controlled-ignition gas-filled dischargedevices insequence-timing circuits. The operation of each such device is dependentuponthe operation of the device preceding it in the cascade arrangement.A single switch in the circuit of the leading de vice therebyeifectively controls the termination of the operation of the entirecascade arrangement.

By providing two such discharge devices, each cascaded upon a singledischarge device and a resistance in the path leading from the single tothe two devices, an effective means for making the operation andtherefore the functions of the two devices, dependent upon each other,is

provided. This desirable construction in. the present invention has beenadapted for both synr chronous and nonsynchronous operation withternating line voltage.

Peaking circuits for synchronizing operation with line voltage have beenused to trigger gridcontrolled gas-filled discharge devices in novel.

arrangements of inverter operated circuits.

current source l2, as at points 20 and 2|.

tension spring 22 may be used to maintain the A novel arrangement ofinductive coils with the sequence-timing circuits achieves simplicity inoperation and economy in construction.

A permanent grid-biasing arrangement has also been provided for insuringstability of opviding a second embodiment of the invention adapted forsynchronous spot-welding;

Fig. 3 is a schematic view of circuits for providing a third embodimentof the invention adaptable for nonsynchronous pulsation and spotwelding;

Fig. 4 is a schematic view of circuits for providing a fourth embodimentof the invention adapted for nonsynchronous spot-welding;

Fig. 5 shows curves illustratin the operation of Fig. 1;

Fig. 6 shows curves illustrating the operation of, Fig. 2;

Fig. 7 shows'curves illustrating theoperation of Fig. 3; and

Fig. 8 shows curves of Fig. 4.

Referring to the drawings in more detail, Fig. 1 shows a weldingtransformer Ill having a prialternating current source l2.Grid-controlled gaseous discharge devices, as, for example, thyratronsl5 and I 6, are connected for firing the ignitrons I3 and M,respectively, in a conventional manner as shown. An operator l1 may bearranged to provide a weld (and no weld) switching arrangement byproviding contacts 18 and I9 on operator I! for selectively connectingor disconnecting thyratrons l5 and [6 from the The contacts I8 and i9normally in the open position as shown. The operator I! may be closed bymeans of a core'23 in a solenoid 24 connected to ;a potential sourceandcontrolled by switch 24'.

illustrating the operation nected in parallel across theserieseconnected.

secondary 28 and rectifier 33. A triggering secondary 36 of a triggeringtransformer 311Wh$6roperation is to be hereinafterdescribed is, in'thisinstance, connected in series in the grid-biasin circuit 21.

Similarly, grid 38 of thyratron IE is normally held at a negativepotential with respectxtocathode 39 by a grid-biasing circuit 40. Thebiasing c-ircuit k lll, has a -transformer-i secondary. M of transformer'2 fieconnected in series with a rectifying device 42 A smoothingcapacitor 43; and ,re-: sistanee A41 are; connected ;in parallel acrossthe serieseconnected rectifiier- 42 and; transformer secondary rl l Thisparallel-connected econstant potential source is connected across thecathode 39,-and -,gri-d 3B.- .-efp;thyratrcnxl6 inseries with atriggering I secondary- 45-of 2 the triggering transformer 31.,Secondary; 4601? the welding trans-- iormerl 0 is connected acrosselectrodes 41 and 48 of a type suitable for passing current through-a.

weld resistance load 49: One, of the terminals 41is.opcratively-ponnected to: adevice 48' for-closingthe-terminals 4'1"and481-with'sufilcient pressure to subject the weld; resistances-load49- :to squeeze load-, thereby producing -suitable welding con-tact. In-thi s:insta;nce, thedevioeABtis a valve arrangement for controlling,a-pressure source suchas air:

source fifi' The cp erator 55 risznormally held in the openposition byatensiorrspring; l In this positiom: valve ;52::is; closedgandnseals "offI the air pressre source 49, and valve 53 is open, permitting escape of;air;pres sure-;fr omthegpressure-achamber fiiyabove the terminalilathrouglrthe outlet 55: In this positiom the compressionspring 56liftsthe term ina l t ll-awayriromgthei welding: load 46.

When the solenoid 51 is energized, operatorflill 'is caused; to, move.;to s. the left; thus; opening 3 the valve causinggairg, pressures;from the; pressure source 49' to force the terminal 41 downruponwthenwelding -loadsi 49-:-at1=; a= proper; weld squeezing pressure. 51 isconnectediby a;line:5i-:thr ough thesecondary Ear-of transformerEiL-whose. primary'fififi. is con-. nectedacross the al-ternatingpotential, source 12'; to the terminalfi L.

64 will normally leave terminals :6 l- :and 462 ;open

because ofthe :tension spring 5 A solenoidafi'o'r; fornloving theoperator M-tothe left isiconnected.

w l sfii s nrlpoint 68. .Line 31 1is :main.- tained at apositiveapotential ,by a. constant lpo 52 and closing the valve 53,thereby;

One side of the energizing solenoid:

The; other side, of the energiz ing .;so,1.enoid 51 is connected-to the.terminal 162.; A contactor, 631,011 a sequence-initiating.operator 5 aansformer]fi-iwhose. primary 1'! is:;con--:

nectedaacrossthealternatingicurrent source .1 2 any.

meanspf inesq-3 If :and ;32.,-:5 Mid-point 18 .nfitthe 7 ans ormer seondaryii 15:;00nne0ted byixlin'a e'lfl si'st-ance 8Tto the negativepotential line 69.

to the line 63 which is thereby maintained at a negative potential withrespect to line 61. A smoothing capacitance 8% is connected across lines61 and 69.

A snuffing condenser 8| in a stand-by and repeat circuit 82 has one ofits sides connected throughpointiw and a" resistance 83 toiline 61. Theother side of" the'snufiing condenser 3! is connected to line 84, oneend of which leads through a resistance til to the positive potentialline 6.1, and the. other end of which leads to anode 850i acontrolled-ignition gas-filled discharge device suchas athyratron 35'.Cathode 86 of thyratron:,85 is-connected through line 86 and re- Agridrbiasingicapacitor 88 in series with a rectifying device 88' is alsoconnected across the resistance '81 betivcen line 86 and the negativepotential line 69. The off-time and repeat circuit 62 has aciditiona'lly-agriii-biasingv capacitor- 96, one side of which is connected tolinePSA-and the other side of which isconnected to line 89 whichleadsthrough repeat switch 89., resistance 91; potentiometer resistances-2 toone end of line 93, the other end of which .runs through variablecontact arm 34 to potentiometer resistance 95 on voltage divider;line-3S; which is connected-between positive and negativepotential lines61 I and 69: The same sidaof igrid-biasing capacitor 96- isalsoconnected through line-:89- toline-fllwhich runs: to anode'98:.-of aroot ingdevice 39 having-w cathode. 566 connected to"point:l 62 on thevoltage divider line 33-.- When a potential 1 first appears betweenlines SLandfiSirom source 51*, the positive potential iofzilineefilappears through resis tance 84 and lineal at anode of the off-time": andrepeat circuit thyratronw85' and the'negative" potential of line 69 willappearthrough resistance 81 and line Beat thecathode-flfiwofthyratron'85 Therefore, as-soon-eas the cathode 86 is warm; thyratron355 willbegin to conduct-through thee circuitconsistingrofline- 61,resistance 84, line: 84-, anode 85; cathode 86", line 66, resistance '81to negativepotential linefis As soon as thyratron 85 begins; to conduct,a potential will appear: acrosszresistancefil between lines86 and 69ythere by causingthe-grid-biasing capacitor 83 to charge: throughrectifier .88 to produce a. normally nega tive :potential at point. I04-with respect to the vpotential. of line'86x Control 'grid-zlfl5 ofthethyra-' tron 89 is connectedxto -a line 106 rleadingufrompoint I04:Therefore, theegrid l05'willibecom'e negative with'respect to thecathode 8%" as soon 'as the thyratron-85 startsto conduct,and,' becauseof 1 the directional nature of the rectifyingdeVice-BB", willnormally'remainznegative' with respect to the cathode 8G despite certainconditions to. be here matter 4 described. When the 'thyratr'on 85"con-- ducts; the: grid-biasing capacitors fl- 'willcharge so aswto-iacquirle azpositive potential on the side "89 and a negativepotential on the side 84 by meansof :the circuiiiz consisting ofpositive potential line 61:: and 'portio'n of potentiometerresistance'95fad justable farmie 4; line" 93, 'potention1eter-resistance92,;resistance 91-; repeat switch 89","line 89, capaci tance QilL L-line84, anode-85,-cathode' 86 lineBSi resistance 81 and;negative'*:potentialline 69? However, the side-89 of' thegrid-biasingcapacitance iwill- .bemaintained at a potentialonly slightly. positivewith respect to 1 line 36' because the side 89 of condenser 9ii isalso"connected through lineotlg line 91 andthe-rectifying device 99 to;point 152 on'-'the'-voltage divider line "96 Therefore, 1 the maximumpositive 'pote'ntial' which the-side 39 of= condehser-avill chargeisapproximately that of point I02 since the drop across the rectifyingdevice 99 is small. Also when the thyratron 85 conducts, the snuffingcapacitor 8I will charge with a positive potential at the point 68 withrespect to 84 through the circuit consisting of positive potential line61, resistance 83, point 68, snufiing capacitance 8 I, line 84, anode85, cathode 86, line 86, resistance 81 and negative potential line 69. i

To start the sequence timer, a switch, as, for example," foot'switchI01, is depressed to close points I08 and I09 of the starter switchcircuit I I which may consistof a solenoid I I I in series with thesecondary II2 of a transformer 3, whose primary II4 may be connectedacross the alternating current source I2, and lines II5 and H6 runningto terminals H1 and H8 controlled by contactor II9 of operator 64 insuch manner that when operator 64 moves to theleft, terminals H1 and II8 are closed and seal off the switch I01. When the foot switch I01 isdepressed, current fiows in the starter switch circuit H0, therebyenergizing the solenoid III and causing the operator I to move to theright against the force of tension spring I20 so as to cause a contactorI2I to open the line I22 and the contactor I23 to close the line I24which has one end connected to point 66 and the other end connected toan anode I26 of a controlled-ignition gas-filled discharge device suchas a thyratron I21 in a sequence-initiating circuit I25. Cathode I28 ofthe thyratron I 21 is connected through the line 86 and resistance 81 tothe negative potential line 69. Since point 68 is connected throughresistance 83 and solenoid 66 to the positive potential line 61, thepotential between lines 61 and 86 will appear across the anode I26 andcathode I28. Also since grid I29 ofthyratron I21 is connected throughresistance I30 and line 89 to the positive side of the grid biasingcapacitor 90, the grid I29 will be slightly positive with respect to thecathode .I28 and the thyratron I 21 will, therefore, when switch I01 isclosed, immediately begin to conduct current from positive potentialline 61 through the sequence-initiating circuit I25, consisting ofresistance 83, solenoid coil 66, point 68, line I 24. contactor I23,anode I26, cathode I28, line 86, resistance 81 to negative line 69.Since the drop in potential across the thyratron I21, when it conductsis relatively small, the potential of point 68 will suddenly drop tonearly the potential of line 86. Since the snuifing capacitance 8Icannot instantaneously discharge, the sudden drop in potential at point68 will thereby cause the potential in line 84 and anode 85 toexperience a large negative drop to a point below the potential of line86 and cathode 86', thereby causing the current flow in thyratron 85' tobe extinguished. This negative drop is shown in Fig. 5 at' the beginningof curve 85, which shows the potential of anode 85 with respect tocathode 86' whose potential is illustrated by curve 86'. Since, asalready pointed out, the grid I05 of thyratron 85' is negative withrespect to cathode 86', the thyratron 85' cannot again conduct, evenafter the snuffing condenser 8| has discharged, and the potentialbetween lines 61 and 86 again appears across the anode 85 and cathode86'. The moment the thyratron I21 is caused to conduct, current flowsthrough the coil 66 causing the operator 64 to move to the left, therebycausing the contactor 63 to close the gap between terminals 6| and 62 sothat current is made to flow from transformer60 toenergize the solenoid6f 51.The operator is made thereby to'move to the left opening valve 52to the high pressure source 49 so as to exert pressure upon theelectrode 41. When operator 64 moved to the left, contactor II 9 closedthegap between the terminals .I I1 and H8, thereby sealing of? the footswitch I01 to prevent sequence interruption by switch I01.Simultaneously, contactor I32 on the operator 64 closes the gap betweenterminals I33 and I34, and a contactor I35 on operator 64 closes the gapbetween terminals I36 and I31. The terminal I33 is on one end of a lineI38'ln weld time circuit I39, the other'end of which is connected to thenegative potential line 69. The terminal I34 is connected to line I40which is also connected to a cathode I4I of a controlledignitiongas-filled discharge device as thyratron I42. One end of line I40 isconnected through resistance I43 to the positive potential line 61 andthe other end of line I40.is connected to the mid-point I44 of secondaryI45 of a timing transformer I46. The secondary I45 is connected inparallel with a series-connected capacitance I41 and rectifying deviceI41 and two series resistances I46 and I49. Mid-points I50 and I5I ofresulting voltage peaking grid-biasing circuit I52 are connected througha resistance I 53 to a shield grid I55 of the thyratron I42. Anode I56of thyratron I 42 is connected by line I51 and resistance I58 to thepositive potential line 61. Grid I59 of thyratron I42 is connectedthrough resistance I60 to point I6I on one side of squeeze-time delaycondenser I62 in the sequence initiating and squeeze-time delay circuit!25. The other side of condenser I62 is connected through currentlimiting resistance I65 to the point 68. The point I 6| on one side ofcondenser I62 isconnected through resistance I66 and potentiometerresistance I61 to the line 93 and through line I68 to anode I69 of arectifying device I10 having a cathode I1I connected by line I 12 topoint I13 on the voltage divider line 96. Because of the rectifyingdevice I10, the point 16! will have a maximum positive potentialapproximately that of point I13 on the voltage divider line 96 fixedslightly positive with respect to line 69. Since the control grid I59 ofthyratron I42 is connected through resistance I60 to the point I6I, thegrid I59 will therefore be at a potential slightly positive with respectto negative potential line 69. When the potential first appeared acrosslines 61 and 69, the squeeze delay condenser I62 is charged with theside 68 positive with respect to the side I6I through the circuitconsisting of line 61, resistance 83, inductance coil 68, point 68,resistance I65, squeeze-delay capacitance I62, point I6I, line I68,anode I69, cathode I1I, line I12, point I13, resistance I19 and negativepotential line 69. At the moment that thyratron I21 started to conduct,the point 68 experienced a sudden drop in potential. Capacitance I62being unable to-instantaneously discharge, the point I6I was forced farnegative with respect to line 60. The control grid I59 of thyratron I42,being con;- nected to point I6I, was thereby correspondingly forced farnegative with respect to line 69. Thus, even though operator 64 causedthe negative potential of line 69 to appear at cathode I 4|, thethyratron nevertheless will not fire. Since the point I6I also becamenegative with respect to line I12, the rectifying device I10 ceasedconducting and the squeeze-delay condenser I62 immediately begandischargingv through the cir-' cuit consisting of line 61, partofresistance 95,

7 adjusting arm .94, line 93, potentiometer resistance I61, resistanceI66, point I6I, squeeze-delay condenser I62, resistance I65, point 68.,line I24, contactor I23, anode I26, cathode I28, line 86,,resistanceBland negative potentiol line 69. The rate of discharge of thesqueezeedelay. condenser I62 is regulated primarily by potentiometerresistance I61.

,The action of squeeze-delay condenser I92 causes a potential pictureat'the grid I59 of thyratron I42 shown in Fig.5 by a curve I59 inrespectpto the potential at the cathode I4I shown by the curve I4I.After the condenser I62 discharges, it will tend to charge in thereverse direction so that grid I59 will become positive with respect tonegative potential line '69. However. the positive potential at I6I islimited by the rectifying device I18 to the potential of point I13 onvoltage dividerline 96 which is only slight- 1y, positive with respectto negative potential line. 69. When the point IISI reaches thisslightly positive potential, the rectifying tube I19 will conduct andprevent further rise in potential. Even though this slightly positivepotential at point I6I appears at the grid I59 so that the grid I59 isslightly positive with respect to the cathode I4I, the thyratron I42will nevertheless still not conduct'because of the potential in theshield grid I55 caused by the peaking circuit I52. The potential at theshield grid I55 may be shown by the curve I55 in Fig. in which it isseen that the shield grid potential is maintained negative with respectto the cathode I II throughout most of a full cycle of. the alternatingcurrent souce I2. The alternating potential of the alternating currentsource I2 may-be shown by. curve E2 of Fig.5. The potential of shieldgrid I55 peaks to zero only once each cycle of the alternating potentialfrom source I2. Therefore, even though grid I59 is, positive in respectto cathode II, the thyratron I42 cannot conduct until the shield gridI55 reaches a peak. The point at which this peak 'is reached withrespect to the alternating potential from source I2 may be adjusted fromaphasing circuit I15.

In one such suitable phasing circuit I15, a transformer secondary I15 ofthe transformer 29, whose primary 39 is connected across thealternatingcurrent source I2 by lines 3I and 32, is connected in serieswith a capacitance I11 and two potentiometer resistances I18 and I19,respectively. One end of the primary I 89 of peaking transformer I49 isconnected at point I8I between the capacitance I11 and potentiometerresistance I18, and the other end of the primary I89 is connected topoint I92 at the mid-point of the transformer secondary I19. Byadjusting the resistance of potentiometers I18 and I19, the point atwhich the peaking circuit I52 will peak may be varied. A fullexplanation of the general operation of peaking circuitssuch as I52, maybe found in the patent application of Dawson and Faulk, Serial No.733,991 filed March 11, 1947, now Patent No. 2,569,720. The firing of'thyratron I42 is, therefore, synchronized by peaking circuit, I52 withthe alternating potential of source I2, and, in this instance, occurs atpoint I55 in curve I55 in Fig. 5.

As part of the weld time circuit I39, the line I51 in the anode I59circuit or" thyratron I92 is connected by line I83 to one side of theparallel connected weld time condensers I84 and I85. The other side ofcondenser I64 is connected by line I85 through resistance I91,potentiometer resistance I 89 I and minimum timing resistance 8 I89 tothe line 93. A'switch arm I90 is, in this instance. arranged to connectthe side, IN 01 capacitance I to the line I86 so that capacitances I84and I85 are in parallel and operate as a single enlarged capacitance,which is desirable in the present instance of pulsation welding. Bymoving the switch armto the point I92, the resistances I81 and I88 areshorted out and the capacitance I85 is disconnected from the circuit sothat a resulting small time constant is achieved; which is desirable forspot-welding operation to be later described. For additional flexibilityin varying breadth of weld time in pulsation welding, a further switchI93 may be providedforshunting outthe resistance at I81 along withadjustment of potentiometer resistance I88.

The weld time circuit I39 also inclues a heat time circuit'i95, acooltime circuit I96 and a weld-triggering circuit I 91. In the heat time"circuit I95, a controlled ignition gas-filled .discharge 'device, asthyratron I99, having an'anode I99 connected by line 299' throughresistance 291 to positive potential line 61, has a cathode 202connected to line 293 which leads'through aresistance 294 totheline I83leading to the anode of the thyratron 'I 42. A grid 295 of the thyratronI98 is. connected to a peaking circuit 296 similar to the peakingcircuit I52 and having a transformer secondary 291 at the transformerI46. The peaking circuit 296 is arranged to produce a varying potentialat the grid 295 shown by the curve 295"" in Fig. 5 wherein peaks occurmid way between the peaks of the 'curve I55. "The mid-point 289. of thetransformer secondary 291 is connected to line 219, one end of whichleads to the anode 2 II of a rectifying device 2 I2 whose cathode 2I3 isconnected to line I12 which is connected to the point I13 which asstated is held slightly positive with respect to the negative potentialline 69. The'other side of the line 2I9 is connected through minimumresistance 214 and potentiometer resistance 215 to the positivepotential line 93. A switch 2I5 which is kept open for pulsationwelding, as in the present instance, may be closed to shunt outthepotentiometer resistance M5 for spot-welding to be hereinafterdescribed. Because of the rectifying device 2I2 connected by line 2I9and point 208 to the grid 295, the potential of grid 295 will beslightly positive with respect to the cathode 292 of thyratron I98 whenthe thyratron I42 is conducting and the peaking circuit 296 reaches apeak. A timing capacitance 2I1- is connected between line 269,leadingfrom the anode I99 of the .thyratron I98, and line 2 I8, one endof which leads to an anode 2 I9 of the rectifying device 2 I2, and theother end of which is connected through a minimum resistance 22'9and avpotentiometer resistance 22I. to the positive potential line 93,.The'line 2I8 is connected to mid-point. 222 of a transformer-secondary223 of transformer I46 in a peaking circuit 224, sim'ilarto peakingcircuit 'I'52,'which'is connected to bias grid 225 of acontrolled-ignition gas-filled discharge device as thyratron 226 inthecool time circuit I96. Anode 221 of therthyratron 228 is connected byline 229 throughresistance 229' to the positive potential'line 61. Asnufiing capacitance 239 is connected between lines-228 and 299 forinverter operation of thyratrons 225 and I98. A timing capacitance 23Iis connected between line 228 andline 2I9 leading to the control grid265- of thyratron' I98:-

Two series-connected voltage dividerresistances-Brand 2.33 are"connected is at the same potential as line I86.

9 across. the anode 221 and cathode 234 of the thyratron 226. Thecathode 234 is connected by line 235 to the negative potential line 69.A midpoint 236 between voltage divider resistances 232 and 233 isconnected to a shield grid 231 of a controlled-ignition gas-filleddischarge device 238, such as a thyratron, in the Weld triggeringcircuit I91. An anode 239 of the thyratron 238 is connected through thecontactor I35 to one side of a primary 240 of a weld triggeringtransformer 31. The other side of the primary 248 is connected to thepositive potential line 61. Grid 24I of the thyratron 238 is connectedto a peaking circuit 242 similar to the peaking cir-' cuit I52 andhaving a secondary 243 of the transformer I46. Cathode 245 of thethyratron 238 is connected to line 246 which is connected by line 241through resistance 248 to. the negative potential line 69. Line 246 isalso connected to cathode 249 of a controlled-ignition gas-filleddischarge device 258, such as a thyratron, in the weld triggeringcircuit I91. Grid 25I of thyratron 258 is controlled by a peakingcircuit 252 similar to the peaking circuit I52 and having a transformersecondary 254 on transformer I46. The peaking circuit 252 hasadditionally a potentiometer resistance 253 for balance control to behereinafter described. The mid-points of the transformer secondaries 254and 243 are connected to the line 241 leading to cathodes 245 and 249.Anode 255 of the thyratron 250 is connected to the positive potentialline 61 by line 256. A snuffing capacitance 251 is connected between theanode 255 of thyratron 250 and terminal I36 in the anode circuit ofthyratron 238 for inverter operation of thyratrons 238 and 258.

Before the thyratron I42 fired, the weld time capacitances I84 and I85chargedthrough the circuit consisting of positive potential line 61,resistance I58, line I83, condensers I84 and I85, point I9I, switch I98,line I86, line 258, anode 259, cathode I1I of rectifying device I10,line I12, point I13, resistance I14, to negative potential line 69. Inthis manner,'condensers I84, I85 charged with a potential positive inline I83 with respect to the line I86. Because of rectifying device I10,the potential of line I86 is normally maintained slightly positive withrespect to the potential of line 69 and, therefore, grid 268 of acontrolled-ignition gas-filled discharge device, as thyratron 26I, in ahold time circuit 262, However, since cathode 263 of thyratron 26I isconnected by line 203, resistance 284, line I83, and resistance I58 tothe positive potential line 61, the

cathode 263 will be positive with respect to the grid 268* whenthyratron I42 is nonconductive and, therefore, the thyratron 26I cannotfire.

'When the thyratron I42 began to conduct current, as explained above,the potential of line I83 dropped to nearly the potential of negativeline 69 thus putting voltage across thyratron 26!.

'However, the drop in potential in line I83, be-

cause of the charge on capacitors I84 and I85, simultaneously forces thepotential of line I86 and, therefore, grid 260 far negative with respectto line I83 and, consequently, cathode 263 and, therefore, the thyratron26I will still be unable to conduct. The potential of grid 269 withrespect to line I83 may be shown by curve 266 with the line I83potential shown by curve I83 in Fig. 5. The condensers I84 and I85immediately begin to discharge through the circuit consisting ofpositive potential line 61, resistance 95,- potentiometer arm 94, line93, resistance I89,

10 potentiometer resistance I88, resistance I81, line I86, capacitorI84, switch I90, point I9I, capacitor I85, line I83, line I51, anodeI56, cathode I4I, point I34, contactor I32, point I33, line I38, andnegative potential line 69. The rate at which the condensers I84 and I85discharge is controlled primarily by potentiometer resistance I88 andresistance I81. 1

In the stand-by condition when potential first appeared across lines 61and 69 and before the thyratron I42 began to conduct, the thyratron 226being connected across the positive potential line 61 and the negativepotential line 69 began to conduct as soon as its cathode became warmthereby charging the snuffing condenser 238 through the circuit composedof positive potential line 61, resistance 20I, line 208, snuffingcondenser 238, line 228, thyratron 226, line 235, and negative potentialline 69. The side 200 of snuffing condenser 238 is thereby chargedpositively with respect to the side 228. Timing condenser 2I1 is alsocharged through the circuit, line 61, resistance 29I, line 290,capacitance 2I1, line 2I8, rectifier 2I2, line I12, point I13,resistance I14, negative potential line 69, sothat the side 288 ispositive with respect to the side 2I8.

The thyratron 250 being connected across potential lines 61 and 69 alsobegan to conduct during stand-by when potential first appeared acrosslines 61 and 69. The snufi'ing condenser 251 is thereby charged duringstand-by with its side I36, positive with respect to side 256. As soonas the thyratron I42 began to conduct, the drop in potential in line I83immediately put potential across the anode I99 and cathode 202 of thethyratron I98 so that thyratron I98 i's'in condition to fire as soon asits grid 295 permits. Due to the peaking circuit 286, the potential atgrid 205 shown by curve 205 in Fig. 5 peaks at point 205"" at thebeginning of the half cycle of the alternating potential I2 followingthe half cycle in which firing point I55 of thyratron I42 occurred.Thyratron I98 thereby begins to conduct at the point 285 When thethyratron I98 begins to conduct, the potential of line 206 sud denlyfalls to nearly the potential of negative potential line 69 therebycausing the potential in line 228, due to the charge on condenser 238,to be forced far negative with respect to line 69 and shown by curves228' and 69, respectively, in Fig. 5. The condenser 230 by this inverteraction extinguishes the thyratron 226. At the same time, by similarinverter action effected by the biasing condenser 2 I 1, the potentialin line 2 I8 is brought far negative with respect to the cathode 234shown by the curves 2I8 and 234, respectively, in Fig. 5. The line 2 I8being connected through the peaking circuit 224 to the grid 225 of thethyratron 226 will cause this low potential with respect to cathode 234to appear at the grid 225. Thus, when the snuffing condenser 23!)discharges quickly and charges with the opposite polarity through thecircuit consisting of positive potential line 61, resistance 229, line228, snufling condenser 239, line 200, thyratron I98, resistance 28 4,line I83, thyratron I42, line 69, and a potential again appears acrossthe thyratron 226, the negative potential at grid 225 prevents thethyratron 226 from again conducting. This is the start of heat time andthe timing condenser 2I1 immediately begins to discharge through thecircuit consisting of positive potential line 61, resistance 95,adjusting arm 94, line 93, potentiometer resistance 22I, resistance 220,line 2I8, timing condenser 2I1, line 200, anode I99, oath ode 292,resistance 294, line I83, line I51,'anode I55, cathode I4I,. point I34,contactor i32, point I33, line I38, and negative potential line 69. Therate at which the timing condenser 211 discharges is controlledprimarily by potentiometer resistance 22! and determines the length ofheat time." When the thyratron I98 began to conduct and the potential ofline 2I8 was forced far negative, the rectifying device 212 stoppedconducting. As the condenser 2 I1 discharges, it will have a tendency toreverse its polarity so that the side II8 will become positive withrespect to the side 259. However, the positive potential at 2I8 islimited by the rectifying device 212 to the potential of point I13 onthe voltage divider line 96.

As soon as thyratron 226 was extinguished, a potential appeared at 235between the Voltage divider resistances 232 and 233. The resistances arechosen so that the potential at 236 will be the same as the potentialappearing at the cathode 245 of the thyratron 238. Thus the shield grid231 will be at the same potential and the thyratron 238 will be incondition to fire as soon as its grid 24I permits. terminals I36 and I31when the operator 84 was forced to the left at the time of discharge ofthe squeeze initiating thyratron I21. Due to the peaking circuit 242,the potential at grid MI is made to appear with respect to cathode 245as shown by curves 24I and 245 of Fig. with the position of peaksdetermined by the setting on phasing circuit I15. Thus, in the halfcycle of the alternating line potential I2 immediately following thefiring of thyratron I98, a peak 24I will occur at the grid of thyratron2338 thereby causing it to fire. The moment thyratron 238 fires, itcauses a sharp increase of current flow through the primary 240 as shownby the curve 249 in Fig. 5. This will, in turn, cause a voltage peak tooccur in the secondaries 35 and 45 of the triggering transformer 31shown by pulse 36 in Fig. 5. This pulse will overcome the negative biasat the thyratrons l5 and it caused by biasing circuits 21 and 40,respectively, so as to make a positive triggering pulse appear at thegrids 25 and 38 thereby causing the thyratron with the proper polarityof line potential across it (in this instance 25) to conduct so as toignite the ignitron I3 and make a pulse of current flow in the Weldingcircuit through. the weld load 49. The pulse of current may be shown bycurve 43 in Fig. 5. 7

As soon as thyratron 233 is fired it causes, by

inverter action on snuffing capacitance 251, the 4 thyratron 255! to beextinguished. The potential in line 255 with respect to cathode 249 willappear as curves 255 and 246 in Fig. 5. The capacitance 251 rapidlydischarges and recharges in the opposite direction through the circuitconsisting of line 61, line 25 snuffing capacitance 251, point I35,contactor 535, point I31, anode 239, cathode 245, line 246, line 241,resistance 248 and negative line 59. When the capacitance 251discharges, suitable firing potential will again appear across thethyratron 25;: so that the thyratron 259 will again fire as soon as thepotential at grid 25! permits. The potential at the grid 25I withrespect to cathode 249, due to the peaking circuit 252, may be shown bycurves 25I and 246 in Fig. 5. Since the peaks at grid 25! are displacedin phase by 180 degrees from the peaks appearing at grid 24I ofthyratron 238, the grid 25I will peak-in the succeeding negative halfcycle of thealternating potential I2 at a point having the same relationas the point at A contactor I35 has closed the 25 which the thyratron235 was caused to fire. The thyratron 255 will, therefore, be permittedtofire at this point 25I in the negative half cycle of alternatingpotential I2. When the thyratron 5 255 fires, it causes an inverteraction on the snuff ing capacitor'251 thus forcing the potential atpoint I39 far negative with respect to cathode 245 (shown by curves I35and 245 in Fig. 5) there.

by creating a potential drop across the transformer primary 248 in thesame direction as the potential drop produced by the firing of thethyratron 233 and of about the same magnitude thereby causing anadditional surgeof current through the transformer primary 253, shown at249 on curve 243 in Fig. 5 which, in turn. causes a positive potentialpulse to appear in the secondaries 36 and 45 of transformer 31, as shownby the curve 35'. This pulse overcomes the negative bias of the biasingcircuits 21 and 49, as previously described, and triggers the thyratronI5 to conduct current to thereby ignite the ignitron I4 so as to cause anegative pulse of current to pass by means of transformer it through thewelding load 49. The negative pulse of current may be shown by curve 49and has the same magnitude and duration as the positive pulse 49 therebyproviding proper balance and efficient operation of welding transformerIii. To insure such proper balance the potentiometer resistance 253 inpeaking circuit 252 has been provided. By adjusting potentiometerresistance 253 the po- .tential curve 25I" may be raised with respect tocurve 246 thereby causing grid 25I to reach a proper firing potential ata point slightly before a peak is reached. Consequently thyratron 259may be adjusted to fire at a point with respect to alternating potential[2 to exactly balance the point of firing of thyratron 233. The positivepulse appearing in the transformer secondary will have a small negativeflare which will have no effect upon the operation of the thyratrons I5and I6 since once the positive portion has caused conduction, currentwill continue to flow thereafter independently of grid potential. When,the thyratron 255 was again caused to conduct, it extinguished byinverter action of snuffing capacitor 251, the thyratron 239, whichitself cannot again fire until its control grid 24! permits.

Assuming the line potential I2 to alternate in this instance at cyclesper second, the thyratrons 259 and 238 may be made to alternately firein the above manner in each successive half cycle thereby causingalternate positive and negative pulses of welding current to flowthrough the welding resistance 49. This alternate firing will continueuntil heat timing condenser 2" has timed out, as shown at point 2I8 inFig. 5, and the peaking circuit 224 has produced a zero peak at the grid225 of the thyratron 226, shownat point 225' in curve 22 5."illustrating the potential at grid 225. Thus, even though the condenser2 I1 has discharged, the thyratron 226 cannot conduct except at theproper point in the cycle of alternating potential I2 determined by theM peaking circuit 224 which, in this instance, occurs at 225. Due tocapacitance 2 I1 and peaking circuit 224, the potential at the grid 225will appear as curve 225" and is normally coincident with curve 205.When the thyratron 226 again conducts at the point 22 5', itextinguishes the heat timing thyratron I98 by inverter action of thesnufiing capacitance 239. The potential of line 200 with respect to line89 and therefore cathode 202 appears as curves 290 and 69 in Fig. 5. Bysimilar action, capacitance 23I forces the potenti'alat line 2| farnegative with respect to potential of line 69 and appears through thepeaking circuit 206 at the grid 205 of thyratron I98 as the drop 205.The cool time capacitance 23I immediately begins to discharge throughthe circuit consisting of positive potential line 61, potentiometerresistance 95, adjusting arm 94, line 93, potentiometer resistance 2 I5,resistance 2 I4, line 2I0, timing capacitance 23I, line 228, anode 221,cathode 234, line 235, and negative potential line 69. The rate at whichthe capacitance 23I discharges is controlled primarily by thepotentiometer resistance 2 I 5. Before the thyratron I98 may againconduct, the capacitance 23I must discharge to point 205" and thepeaking circuit 206 must have eiiected a peak at grid 205 afterdischarge of capacitance 23 I, in this instance shown by the point 205".

As soon as thyratron 226 began to conduct, the potential in line 228dropped to nearly the negative potential of line 69 which, due toresistance 248, is lower than the potential at line 246. The shield grid231 of the thyratron 238, being connected through point 236 andresistance 232 to line 228, will thereby have a correspondingly lowpotential. Thus, the shield grid 231 will prevent the thyratron 238 fromfurther conduction. Thisnegative biasing potential on the shield grid231 may be shown by curve 231 in Fig. 5. It is seen that when thisbiasing potential occurs in shield grid 231, if the thyratron 238 isconducting, it will continue to conduct until extinguished by theconduction of thyratron 250 after which it can no longer fire. If thethyratron 238 was already extinguished at the time the biasing potentialin 231 occurred, it cannot again be triggered to conduct peaking circuit242. Therefore, it is seen that the welding current during "heat timewill always begin with a pulse of one polarity 49 and will always endwith a pulse of the opposite polarity 4'9" with only an even number ofcurrent pulses occurring during heat time thereby equalizing thepositive and negative pulses through the transformer I0.

After the cooling time determined by the discharge of condenser 23I andthe peaking circuit 206, the thyratron I98 will again be made to conductto repeat the cycle of heat and "cooling times explained above. Whilethis repetitive action continues, the weld timingcapacitors I 84 and I85discharge as shown by curve 260", thus 'efiecting the same potential atthe grid 260 of the thyratron 261. It should be noted here that when thethyratron I 98 conducts, it

causes current to flow through the resistance 204 thereby effecting apotential rise in line 203. The resistance 204 is chosen so that thepotential rise in line 203 will be of such a magnitude that thepotential at the cathode 263 will be higher than the maximum possiblepositive potential at the grid 260 of thyratron 26I. The maximumpositive potential at the grid 260 is determined by the line 258 whichleads to the rectifying device I whose cathode is connected to the pointI13 by line I12 on voltage divider line 96. Therefore, if the thyratronI98 is conducting, even though the capacitances I84 and I85 have timedout, the thyratron 26I cannot fire until the thyratron I98 isextinguished. The rise in potential of cathode 263 when the thyratronI98 conducts current through the' resistance 204 may be shown by curve263' in Fig. 5, and in a similar manner, if thyratron I98 isextinguished and the thyratron 26I conducts, it causes current to flowthrough the resistance 204thereby-effecting a potential rise in thecathode 202 which is morepositive than the maximum possible positivepotential in grid 205 thereby preventing the thyratron I96 fromconducting after the thyratron 26I has started to conduct. Thus, ifthyratron I98 is conducting when the weld time capacitances I84 and I85time out, as in this instance shown by curve 260, the thyratron I62 willWait until the thyratron I98 is extinguished by inverter action ofthyratron 226 after which it will conduct at the point 263" therebypreventing the thyratron I98 from conducting thereafter. Note that thisarrangement does not permit cutting short of any heat time period andinsures an integral number of full heat time" periods.

The hold time circuit 262 has additionally a hold time capacitor 210connected between lines 265 and 2H. One side of line 21I is connectedthrough resistance 212 and potentiometer resistance 213 to the positivepotential line 93, and the other side of line 21I is connected throughresistance 214 to grid 215 of sequence terminating circuit 216. Line 21Iis connected by line 211 to anode 218 of rectifying device 99 whosecathode I00 is connected to point I02 of the voltage divider line 96thereby limiting the maximum positive potential at 21I to approximatelythat of the point I02 which is slightly positive with respect to line203 when thyratron 26! is conducting. The other side of the capacitance210 is connected by line 219 through resistance 269 to the line 28I, oneend of which is connected to cathode 282 of the thyratron 2-83 and theother end of which is connected through capacitance 284 and line I06 tothe point I04 between capacitor 88 and rectifying device 88 in the offtime and repeat circuit 82. During stand-by, the capacitance 210 chargesthrough the circuit consisting of positive potential line 61, line 266,capacitance 210, line 211, anode 218, cathode I00, point I02, resistance285, point I13, resistance I14 andnegative potential line 69 so that theside 266 is positive with respect to the side 2'. When the thyratron 260started to conduct, because of the charge on capacitor 210,

the line 21I was brought far negative with re spect to negativepotential line 203, when thyratron 25I. is conducting, thereby producingat grid 215 the same negative potential. At the same time the cathode282 is brought to the potential of line 266 in the anode circuit ofthyratron 26I which is nearly at the negative potential of line 263 whenthyratron 26I is conducting. Thus, the thyratron 216 is ready to conductas soon as permitted by its grid 215. "Hold time" condenser 210immediately starts to discharge through the circuit consisting of thepositive potential line 61, resistance 95, adjusting arm 94, line 93,potentiometer resistance 213, resistance 212, line 21I, hold timecapacitance 210, line 266, anode 265, cathode 263, line 203, resistance204, line I83, line I51, anode I56, cathode I4I, point I34, contactorI32, point I33, line I38 and negative potential line 69. The rate ofdischarge is controlled primarily by the potentiometer resistance 213.

The potential picture at control grid 215 with respect to cathode 282may be shown by the curves 215 and 282, respectively, in Fig. 5. Whenthe control grid 215 reaches a potential slightly positive with respectto the cathode 282, the thyratron 283 will discharge so as to causecurrent to flow through the resistance 280 thereby effecting a potentialrise in 28I which appears through capacitor 284 and line I06 to overcomethe negative biasing potential at grid I05 of thy- 15 ratron"85' therebycausing thyratron 85' to fire. When.;thyratron 95 fires, capacitance 8|extinguishes thyratron I21by inverter action. At the same timegrid-biasing capacitance 90 causes grid I29 to be forced far negativewith respect to the potential of the cathode I28. Thus, while thesnuffing capacitance 8I discharges rapidly because of a low'timeconstant, the capacitance 90 will prevent thyratron I21 from againfiring. When thyratron I21 ceases to conduct, the coil 58 is deenergizedand tension spring 85 moves the operator 64 to the right, therebyopening contacts at 93, I19, I32 and I35. By this action solenoid 51 isdeenergized and pressure on electrode 41 is removed; conduction throughthyratron I42 and cascaded thyratrons 281 and 283 is stopped;-terminalsI35 and 131 are opened so as to insure against possible firing ofthyratron 238.

' If the foot switch I01 is in the open position when thyratron I21 isextinguished so that terminals I98 and I09 are open, solenoid III isdeenergized and tension spring I20 moves operator I20 to the left,opening line I24 and preventing "the thyratron i2! from furtherconducting and the ap aratus is again in position ready for anothersequence, as explained above.

If foot switch I01 is in the closed position so that points I08 and I99are closed, the solenoid III remains energized and the line I24 remainsclosed by contactor I23, and thyratron I21 will conduct to start anothersequence, as explained above, when capacitance 99 has discharged throughthe circuit consisting of positive potential line 51, resistance 95,adjusting arm 94, line 93, potentiometer resistance 92, resistance 9I,repeat switch 89, line 89, off-time capacitor 90, line 84, anode 85,cathode 89, line 06, resistance 81, and negative potential line 69. Therate of discharge of off-time capacitor 99 is controlled primarily bypotentiometer resistance 92.

If repeat switch 89 is switched to point 89" so that line 89 is open infront of resistance 9 I, and if the foot switch I91 is held in theclosed position so that inductance coil III is energized leaving lineI22 open, the off-time capacitor 90 cannot discharge, and thereforeprevents the thyratron I21 from conductingindefinitely. By means of thisfeature, the repetition of the sequence may be prevented until the footswitch I01 is raised, thereby deenergizing the coil I i I and causingline I22 to close, and discharge off-time condenser 90 through thecircuit consisting of line 84, line I22, contactor I2 I, point 89",switch 89, line 89, and condenser 99. The line I24 being open, thyratronI21 cannot again fire until the foot switch I81 is depressed.

The rectifying device 88 effectively prevents an unwanted phenomenonfrom occurring. For example, when the switch !01 is depressed and lineI24 is closed, thyratron I21 fires and extinguishes thyratron 85. If thecontactor I23 bounces, as contactors often do, the line I24 ismomentarily open thereby causing the thyratron I21 to be extinguished.The biasing capacitance 90 has acquired suflicient charge through theline. 91 from rectifying device 99 to permit the thyratron I21 to refirewhen the bouncing contactor I23 again closes the line I25. However, ifthe rectifying device 88' were not present, the bias on grid I may havebeen lost during this small bouncing interval when both thyratrons I21and ,85' were extinguished so that thyratron 85' may "refire therebypreventing the thyratron I21 from again refiring ,and' the sequencesticks until the l6 capacitance; 99- is again discharged, as explainedabove. By inserting the rectifying device" 94, loss of charge of biasingcapacitance 93 is prevented thereby preventing the unwanted reiiring ofthyratron and neutralizing the bouncing effect of contactor I23.

The above described apparatus may be used for spot-welding by moving theswitch arm I to the terminal I92 and thus disconnecting the capacitanceI85 and shunting out resistances I81 and I88. In such case, thecapacitor I84 is discharged very rapidly. The thyratron 26| in the holdtime circuit 262 thereby becomes ready to fire before the end of thefirst heat period and waits, as explained above, while the thyratron I98is conducting. ,As soon as the thyratron I98 is extinguished at the endof the heat period, the thyratron 251 immediately conducts causingcurrent to flow through resistance 204 so as to raise the cathodepotential of thyratron I98 to a point where it cannot refire, asexplained above.

Briefly summarizing, the sequence of operations described above is asfollows:

1. Foot switch H31 is closed to energize solenoid III thereby movingoperator I28 to the right.

2. The thyratron I21 in the sequence-initiating and squeeze delaycircuit conducts and energizes the inductance coil 65 thereby moving theoperator 54 to the left, at the same time extinguishing thyratron 85' inthe off-time and repeat circuit '82.

3. The contactcr 53 causes solenoid 51 to be energized; contactor II9seals in switch I01 to make the circuit non-beat; contactor I32 closesthe cathode circuit of thyratron I42 in the weld time circuit I39; andcontactor I35 closes the anode circuit of thyratron 238 in thetriggering circuit I91.

4. After squeeze delay, thyratron I42 conducts starting weld intervaltiming and applying voltage to thyratron I93 in the heat time circuitI95.

5. Thyratron I98 conducts at zero voltage with respect to line atthe-start of the half cycle following the one in which thyratron I42started conduction. Thyratron I98 extinguishesthyratron 225 in the cooltime circuit I95 which allows the shield grid potential in thyratron 238to rise to-the same potential as its cathode 245, thus removing shieldbiasing from thyratron 23B.

6. At the proper point in the half cycle as determined by the phaseshift heat control circuit I15, the thyratron 239 conducts, generatingtriggering voltage in the secondaries 36 and 45 of transformer 31, andat the same time extinguishing thyratron 258.

'1. Inthe next half cycle, thyratron 250 becomes condu-ctive at anidenticalpoint in the half cycle as the thyratron 239 did in thepreceding half cycle, and extinguishes the thyratron 238 and. causesanother triggering pulse to appear in the secondaries '35 and 45 oftransformer 31. This inverter action continues until the end of thefirst heat period.

8. At the end of the heat period, thyratron 226 again conducts,extinguishing thyratron I98 and returning biasing voltage to the shieldgrid 231 of thyratron 298 to stop the-inverter action of the triggeringcircuit I91.

9. At the end of cool time, thyratron I98 again conducts and the cyclerepeats until th weld interval times out. i

10. The weld interval having timed out, if

during a cool time, thyratron 261 in the "hold time circuit 262immediately conducts. If during a heat time, thyratron 261 waits untilthe end of the heat period and then conducts ending the weld interva andstarting, hold time.

11. At the end of hold time, thyratron. 283, in the sequence-terminatingcircuit conducts and. pulses the grid of thyratron 85; which conductsand extinguish'es thyratron .I2'lwhich-per mits the operator 64 to moveto the right:

12. If set for spot operation,- step 9 above is omitted and thethyratron 26I conducts imme-- 10 diately after. the end of thefirstheat. period.

Itshould be noted that by connecting the anode circuit of one: thyratronto the cathode circuit of a; succeeding thyratron, as illustrated bythyratrons I42, 26Iand 283; a very: useful'cascade arrangement is obtainedwhereby the current howin the entire cascade arrangement .may be ex-=-tinguished from av single switch in the circuit ofthe leading thyratronthereby resetting the whole arrangement. Such an arrangementalso'permits the useof a simple resistance; as resistance 2%, in the cathode,circuits of succeeding thyratron's-for controlling the point of firingof'the' succeeding;

thyratrons; i V V Theinductance coil- (it-besides: controlling o'per'ator 64' is arranged to serve another'useful' pun pose. When' thethyratron I21 is extinguished; the currentin, the highly inductive:c'oil 66 is cut ofi rapidly. This causesi a:- rise 1 of: inductive voltage: in: the coil' whichv is kept: Within reasonable limits byresistance8'3 l This rise makespoint 6% highly positive and is in:series With lithe. circuit charging squeeze delay capacitance I62v whichmust be: completely recharged? duringv on time; Consequently,capacitance I621isrecharged very rapidlywith the resi'stancelfifibeinginserted to prevent overchargingt This isone of the factorscontributing tothe high speeds obtainable in the. present invention;Forj example, in spot-- welding, 400 spots perminute may be, obtained. 5

The other timing capacitances have longer pe: riodsin whichto recharge;t

The unit: isself-compensating; fplf linje voltage variations; Forexample, the value; of ;charge' ol i a a en ma imQi QnQ hevoltagebetween line: 61 and; point p I I12 which is: afunction ofvoltagebetween; lines; {51; and 6 9 The discharge of capacitance 21)];fer-timing de-r scribed above. is al'so a tuhctidnbt the voltagebetween. lines. 6']; and- 69;. Consequently, ir the line voltage is.low,,,the original charge on--capac i tance" 2707 is low,. but since'the discharging vo1tagewill'also'be'low, the same timing will res ulta gThe potentiometer resistahceL5 is provided to, compensate, for?eirample,v for tolerances iniparts; by providing aslightvariation-inithe'discharge voltage. i 7

From the above" operational description it is"v noted that the techniqueof: driving} bothf grid and cathode of a th ratronnegatives'imiiltaneously has been extensively u'sedi A" contribute; ingfactor to the high stability. achieve'd in this" type, r operation isthe; provision'offaj'capacit directly across the grid: andcathodein'ci'rcui which duringgstand-by, brinsgthefpositiye pct tia'lf of ii e61" to the I cathode and harge these? capacitors so as to maintain thegrid? rie with respect to the cathode. Such arrange maybeseen,forexa'mple inthyratronsflfl 2 and 283iwhere thecapa itorsreinamunnumbered."

In a second embodiment of the "presentT invenY- tion; the" portion- 290iii Fig} 11 blocked in l n ie e ce ib 21 n'fiiZiOiwm S IE FQW: F"W 1@1g; e d? s uence t -merz Inthis embodiment, the'triggering circuit 29'-Ire- 7 18 places the triggering and heat and cool time circuits I97, Iand I96. In the triggering circuit 29I, controlled-ignition gas-filleddischarge device 292, such as a thyratron, has anodev 293 connected byline 294 through resistance295' to the posi ive potential line segmentii'iwhich is connected to the rest of the positive potential line 647 atpoints a and b. Cathode 296 is connected through line 29? to thenegative potential limit! at the pointe and grid 298 is connected to agrid biasing peaking circuit 299 which is preferably similar to thepeak-ingcircuit I52. The secondary 365: of transformer Hit in thepeaking circuit 29% has its midpoint tti connected to line 291 runningto cathode 295. Point 302 in the output of the pea-king circuit 299mconnected by line3il3 at the point d running to the shield grid I55 ofthyratron itgin thev Weicltime circuit I39. Line 394 is insertedbetweenpoints e and f, and line 305 is insertedbetween g and h toinclude the transformer secondary 28 in the grid-biasing circuit 27. A

controlled-ignition gas-filled discharge device 386,

such as-a thyratron has an anode 307 connected by means of points 308and 309 and contactor 3H2 of operator 64 through a resistance 3I I topoint i in the primary 2% of triggering transformer 37. Theother side ofthe primary 2 40 is connected at oint 1 to linefii. Cathode 3I2 isconnected to thepoint3I3in1ine3I4.

The line3I4 is connected at pointk to line 263' running to cathode 263of thyratron 72%| inthe"hold time circuit 262. The other end of 3I druns to point 3I3 which is connec.ed through resistance 3H3, line 3H5,point 3H, and point 1 to the anodeIEfi of thyratron I42'in the weld timecircuit i39; The anode I56is also'connected through resistance SIB tothe positive potential line 6?; Grid 3119 of thyratron 356 is connectedby line 323 to the output of peaking circuit 32! which is preferablysimilar to the peaking circuit 252 and has an adjusting potentiometerresistance 322- forraising and'lowering the output potential form ofpeaking circuit 32!. Mid point 323' of secondary 324 of transformer I48is connected by line 325 through point 3I3 to cathode 3I2 of thyratron306'. Point 326 inthe line 3H5 is connected by line 321 throughvthepoint m' to shield grid i328 of the thyratron 26!. Point'329 of line 321is connected through capacitance 336, resist- 0 ance 33I-,and=potentiometer resistance332 to the positive-potential line segment93' whose ends are connected to the rest of line 93 at'poihts n ando.Point 333 between resistance 33! and capacitance 33D-is;connected.at thepoint p tovthe grid 25% timer is first turned 011;. the potentialbetween lines-61;, and 69 appears across the thyratronetil in thetriggering circuit'zti; becauseoflines 29 and- 2971 The thyratronzezwin, therefore, con-' duct during stand-by and will charge thecondenser 33'!" with the point iteipositivewith respectto the line'29 l.

thyratron I i-2 will, nevertheless," be kept 'fronifir ing by thenegative potential at its 'shield' grid from the peaking transformer 299, Whiclimay be When the conden er I $2 has timed? out, as shownati551" iii-Fig; 6','t1-;e"

19 shown as curve'l'55 in Fig. 6. In the next half cycle of thealternating potential I2 after the squeeze-delay capacitor I62 has timedout, the peaking circuit 299 will produce a peak at a point I55determined by a point selected by a setting on phasing circuit I therebypermitting thyratron I42 to fire. The weld time capacitance 330 had,during stand-by, charged through the circuit'consisting of line 61,resistance 3I8, point 3I1, line 3I6, point 326, line 321, point 329,capacitance 336, point 333, point p, line 258, anode 255, cathode Il'I,line I12, point I13, resistance I14, negative potential line 69 so thatthe side 329 is positive with respect to the side 333. The instantthyratron I42 is fired, because of the charge on capacitance 339,potential of point 333 and therefore grid 269 of thyratron 26! is forcedfar negative with respect to the potential in line 3I6 and cathode 263so that thyratron 26I cannot fire, even though the firing of thyratronI42 created voltage across the thyratron L The potential of grid 266with respect to line 3I6 is shown by curves 260 and 3I6 in Fig. 6. Theweld timing condenser 336 immediately begins to discharge through thecircuit consisting of line 61, resistance 95, adjusting arm 94, line 93,potentiometer resistance 332, resistance 33!, point 333, condenser 330,point 329, line 321, point 326, line 3I6, point 3I1, point Z, anode I56,cathode I4I, point I34, contactor I32, point I33, line I38, and negativepotential line 69. The rate of discharge of the weld time condenser 336is controlled primarily by the potentiometer resistance 332.

The firing of thyratron E42 with its consequent drop in potential ofline 3I6 thereby also puts voltage across the thyratron 306. The points309 and 368 have previously been closed by the contactor 3I6 of theoperator 64 when induction coil 66 was energized. The thyratron 306 is,therefore, ready to fire as soon as permitted by the potentialof itsgrid 3 I9. The potential on the grid 3I9, due to the peaking circuit32I, appears with respect to cathode 3I2 as curve 3I9 in Fig. 6 and hasa phase relation causing peaks to occur 180 degrees from the peakscaused by the peaking circuit 299 shown by curve 298. Therefore, in thehalf cycle of line potential I2 following the firing of thyratron I42,the thyratron 306 will be permitted to fire, as at point 3I9'. Thefiring of thyratron 366 will extinguish, by inverter action of condenser331, the thyratron 292. This action is shown by curve 264 showingpotential of line 266 with respect to cathode 296. At the same time, ahigh current rise occurs in a transformer primary 240 thereby producinga positive peak in secondaries 36 and 45 of transformer 31 shown bycurve 36. Due to the peaking circuit 299, the thyratron 292 will againbe permitted to conduct at an identical point 298 in the next half cycleof alternating potential I2 thereby extinguishing the thyratron 238 andproducing another positive peak 36' in transformer secondaries 36 and45. The inverter operation of the triggering circuit 29I will continueto produce peaks in the positive and negative half cycles of thealternating potential source I2 to cause welding current pulses 49through the load resistance 49, as explained with regard to triggeringcircuit I91 in the first embodiment, and will continue until thyratron26I fires. When the capacitance 330 times out as at point 260, thethyratron 26! is ready to fire and will fire immediately if thethyratron 306 is extinguished thereby passing current through resistance3I6 which raises the potential of cathode 3I2 above the maximum positivepotential which may appear at the grid 3I9 so that thyratron 396 cannotthereafter fire. If the thyratron 306 is conducting at the time thecapacitance 303 times out, as in the present instance, the thyratron 306will cause current to flow through resistance 3I5 thereby raising thepotential in line 3 I 4, shown by curve 3I4. Therefore, cathode 263 ofthyratron 26I will be above the maximum positive potential that mayappear at the grid 260, thereby making the thyratron 26I wait until thethyratron 306 is extinguished before the htyratrcn 26I is permitted tofire. By means of this feed-back arrangement through resistance 3I5, itis seen that only an even number of current pulses will be caused toflow in the welding transformer I6 and the operation will automaticallybe full cycling. The other operations in the sequence have beenheretofore explained with regard to the first embodiment.

In a third embodiment, the invention forms a non-synchronous pulsationand spot-welding timer by removin the portion enclosed in the brokenline 340 and inserting the portion 340 in Fig. 3. In this embodimentapulsation timing circuit MI is inserted in place of the triggering andpulsation circuits in the first embodiment. In the pulsation circuit 34Ia cool time circuit 342 has a controlled-ignition gas-filled dischargedevice 343, such as a thyratron, having an anode 344 connected by line345 throughresistance 346 to positive potential line segment 61 whoseends are connected to the rest of line 61 at points a and b. Cathode 348is connected by line 349 to negative potential line segment 69 whoseends are connected to the rest of line 69 at points 0 and 20. Controlgrid 350 of thyratron 343 is connected through resistance 35I, line 352and timing capacitance 353 to line 354. 'Line 352 is connected throughresistance 355 and potentiometer resistance 356 to line segment 93 whoseends are connected to the rest of line 93 at point n and 0. Line 352 isalso connected by line 351 to anode 358 of rectifying device 359 havinga cathode 366 connected to line segment I12 the ends of which areconnected to the rest of line I12 at points a: and :11. Anode 344 isalso connected by line 345 through a snuffing capacitance 36I to line354 leading to anode 362 of a grid-controlled gaseous discharge device363 in a heat time circuit 364. The anode 362 is' connected through line354, resistance 365 and solenoid coil 366 to positive potential line 61.Cathode 361 is connected to line 368, one end of which leads throughpoint It to line 203 leading to cathode 263 of thyratron 26I in the holdtime circuit 262. The other end of line 368 leads through resistance369, line 310 and through point 1 to the anode I56 of thyratron I42 inthe weld time circuit I39. Shield grid 31I of thyratron 363 is connectedto point 312 in line 313 which is connected to line 314 leading from theline 310 to the shield grid-326 of thyratron 26I in the hold timecircuit 262 through the point m. The point 312 is connected to one sideof parallel condensers 315 and 316; the other side of condensers 315 and316 may be connected in parallel by switch arm 311 to the line 318leading to the point p in the grid 260 circuit of thyratron 26I. Theline 318 is connected through resistance 319, potentiometer resistance330, and minimum resistance 38I to the positive potential line 93.Resistances 380 and 319 may be shunted out by line 382,- point 383, andswitch arm 311. The resistance 319 may be shuntedout by'con- :nectingswitch arm 384 to the point 385. Grid asmair 386 of thyratron 363 is.connected through reland potentiometer resistance 3.9.2 to line 93..Also. line 398 is connected through line- 39.3 to anode.

394 of rectifying device 359. The. line: 395 is.in'- serted to connectpoints z and a. of; line 911:, the line 396 is inserted to connect the;point. b and c of line we and line 453 is inserted. to connect points aand h: of line 258. Any suitable con-- tactor 3.91, for connecting,alternating; current source I2 to the weld load 49:, is connected. by1ine398 to the. point ct andby'linez399to poi-ntzef. The contactor3.9.1. is controlled. at points: 43.91 and 40.! which may be: closed andopened by opera-tor 402 operated by the. solenoid. 3.6.6..

During stand-by, the potential betweenlines 61 and 69 appears across thethyratron. 343,. whose grid 356 being slightly positive in respect toits cathode 33, because of connection through rectifying device 359 toline I12, will make thyratron 343 normally conductive, Thesnufiingcondenser 36! will thereby be charged through the line 61,solenoid 366, resistance 365, point 354, snufiing condenser 36!, line335, anode 344, cathode 3481, line 339 and negative potentialline 69with the side 353 positive with respect to the side 345-. Because ofrectifying device 359, line 389 and therefore grid- 363 of thyratron363-wil1 be slightly positive with respect to line 39 during thisstand-by conduction of thyratron 343. Also during stand-by, thecondenser 353 in the heat time circuit 364 charges through the circuitconsisting of positive potential line 61, inductance coil 366,resistance 365, line 354, capacitance 353, line 351, anode 358, cathode369, line 112, point I13, resistance ift i. and anode potential line 63so that the side, 35,3 is positive with respecsto the side 351'.

the circuit consistingof line 6.1 line. 3.13,, 1ine 314, line 3-13,:point 312, capacitances 3 15. and. 316, switch. arm 311, line 318, pointp, line 2.58,.

sistance I13, andnegative potential line, 69. so that the point 312 ispositive with respectto the,

line 318; During stand by, the positive potential of, line 61 appears atcathode 3610f thyratron- 363 in the heat time circuit 364through the;circuit fi'i, line 3.10,resistance 3.69, linev 3,69, cath ode 331 sothat the-thyratron 363 willnot fire:

While thyratron I42. is non-conductive. The instant-the thyratron I42fires, the. potential'in-line 31!). drops, thereby putting, voltageacross. the

thyratron 35,3, and at the same't'ime, because. of capacitances 316and.3.1.5., carries the potential at grid 269 for thyratron 26l intheweldtime circuit 26.2 far negative-with respect. to line 316 andtherefore cathode 2.63;. This may beseenin Fig. 7 by the curve 266 whichrepresents thepotential of the grid 26!! and the curve 310 which ance95, arm 94,,line 93, resistance 3'81, potentiometer resistance 383,resistance 319; line 318,

capacitances 315 and 316,1point 312', line 313', line 314, line 310,point Z, anode $56, cathode M1;

point I33, contactor i 32; point I33, line 138; and" negative potentialline 69-. At theemoment that the potential in line 310 dropped,"therebycans-- During stand-by, the weld time? interval condensers 315and 316' charge. through heat time and startin @001 time",

22-. ing. voltage to appear across; the thyratron. 363,. the thyratron363.conducts; When thyratron 363; conducts, it. causes current to; flowthrough the. inductance coil 366. so as: to: make the; operator 492 moveupward,,;ther.eby closing: the gap" be.- tween the points: 30.0- and4.0I'to operate; the contactor 391. so as topermit current. tov flowfrom. the alternatin current source. 42 through the weld load 43. At.the; instant the thyratron: 363 begins to conduct, it also causes, byinverter action of capacitance 361, the thyratron 33:4- to, beextinguished. The potential. picture in line; 3.45 leading to the anode344. of. thyratron 343 is" shown by the: curve 345 in. Fig; '7. Thepotentialv there shown. is with respectto the potential at thecathode343. shown. by the curve 343". Be.- cause of the charge onthevcap'acitanc'e 353;. explained: above, theinstant thyratron: 363- conducts, the grid: 359 of the thyratron. 3.43: is forced far negative withrespect to the cathode 3481,. as. shown by the curves 356- and3.48,.respective1y', in Fig. 7.. Therefore, even though capacitance 3.6I; rapidly discharges because of. a 10W time con-- stant, thecapacitance 35.3 preventsthyratron343 from. again. firing unti1 thecapacitance 353 has.

discharged to a point where the. grid 315.9: Willbe slightly positivewith. respectto. the. cathode 348; The capacitancev 353 immediatelybegins to discharge through. the circuit; consisting of line 61,;

. resistance 95, adjusting arm 94, line: 93;..potentiometer.resistance-.356, resistance 355 line 3512, capacitance 353$, line13545,.anode 362; cathode-3:61,, line 368'; resistance-36.9,. line13i10;. point1,. anode; I56, cathode I!3i,.pointi 1.34:,contactor I32, point 833;lineE38,.andnegative.potential-line-fifii. The

rectifying device 359rconnectedg to, theline 352:; prevents thecapacitance: 353: from. recharging. in. the opposite directionbeyondapiotentialslightly higher than negative. potential line; 69;.Thyra' tron 333 will; again conduct whencapacitance 353. discharges to.point 35.0" where the grid 3,59 becomes slightly positive.- withrespectto the p o tentialat cathode 398;. Whenthe thyratron 333 again fires, itextinguishes thyratron 363 by inverter action of. capacitance36i therebyending Thepotential. in line 354 leading to; anode; 36% withre.- specttoline 3:1Bis shown by curves 35,4 and; 3.,16, respectively. When the.thyratron 343; fires; because cf the charge on; cool time? capacitance389,. grid 38.6 of. thyratron 363 is-forced: far; nege ative with.respect toxthev potential of line 313. Cathode 3.61; being at thepotential of line 313, thereby prevents refiringrofv thyratron 363,.even though capacitance. 361 has, rapidly discharged"v and recharged inthey opposite direction; as at 33. 3. Current how will cease; ininductance coil 363 and operator, 332 will; drop'backto stopcurrent flowto thevveld load 49. The-resulting,potential.

picture of the control grid 3'86jissh0wnby curve 336? with; respect topotential. 316.. Thecool time condenser 389, immediately begins to checharge through the circuit: composed ot line 31',

resistance 95,- adjusting arm: 94, line 93, potentiometer resistance392; resistance 39;! capaeig tance 339, line 333, line;..3.45, thyratron3.3.3.;line:

339, and negative potentialline 69;.atca1rat'e, con;-. trolled primarilyby the potentiometer resistance the cycle will berepeated. The cycle, asex plained above, will continue to repeat until weld interval capacitors315 and 316: time out ace-- cording to the curve 260 to. 260 where the'grid 260* of the hold' time thyratron 26 I2 becomes-z slightly positivewith respect to cathode 263 and thyratron 26I may fire. If the weldinterval capacitances 315 and 316 time out while thyratron 363 isfiring, the thyratron 26I will, nevertheless, be unable to fire becausecurrent from thyratron 363 flowing through resistance 369 will causecathode 263 to rise in potential to a pointabove the potential ofcontrol grid 266, as shown by the curve 263. Thyratron 26I willtherefore wait until heat time ends and thyratron 363 is extinguished,at which time the thyratron 36I will immediately fire, thereby causingcurrent to flow again in resistance 369 raising the potential of cathode361 above the maximum possible positive potential of grid 386 so thatthyratron 363 will be unable to fire again and the weld interval isended. It is seen, as explained earlier, that this feed-back arrangementwith the resistance 369 insures an integral number of full heat periods.

This embodiment is also adaptable to spotwelding, for example, bydisconnecting capacitance 316 by means of switch 311 being connected topoint 383, and also thereby shunting out resistances 386 and 319. Thetime constant is reduced to where capacitance 316 times out before thefirst heat cycle ends, thereby making thyratron 26I fire immediatelyafter thyratron 363 is extinguished at the end of the first heat cycle.

In a fourth embodiment, the portion enclosed in dotted lines 346 isreplaced by 465 of Fig. 4 to form a non-synchronous sequencespot-welding timer, In this embodiment, the weld time" capacitance 466is charged during stand-by through the circuit consisting of linesegment 61, which is connected at points a and b to the rest of line 61,inductance coil 461, resistance 468, line 469, capacitance 466, line4I6, point p, line 258, rectifying device I16, line I12, point I13,resistance I14, and negative potential line 69 so that the charge at M6is negative with respect to the charge at 469. When the capacitance I62timesout, thyratron I42 fires, thereby causing the potential in line469, which is attached at point Z to anode I56, to drop, thereby forcingthe potential of the control grid 266 far negative with respect tocathode 263 as shown by the curves 266 and 263 in Fig. 8. Also currentwill be made to flow through the solenoid 461 so as to cause theoperator 462 to close the gap between the points 466 and 46I therebycausing contactor 391 to connect a current source as, for example,source I2 through transformer I6 to the welding load 49. The capacitance466 begins immediately to discharge through the circuit consisting ofline 61, resistance 95, adjusting arm 94, line segment 93, which isconnected at points n and o to the rest of line 93, potentiometerresistance 4, resistance 4l2, line 4I6, capacitance 466, line 469, pointI, thyratron I42, point I34, contactor I32, point I33, line I38, andnegative potential line 69. When the capacitance 466 discharges to thepoint 266 where grid 266 becomes slightly positive with respect tocathode 263, thyratron 26I discharges thereby causing current to fiowthrough the circuit, consisting of line 61, solenoid 4i3, line 4I4,resistance 4I5, point q, line 266, thyratron 26I, line 263, point k,line 469, point I, thyratron I42, point I34, contactor I32, point I33,line I38 and negative potential line 69. The current in solenoid 4I3being in a direction opposite to that of solenoid 461 causes aneutralization of fields, thereby causing operator 462.120 fall backanddisconnect the points 466 24 and MI so as to end the 'weld interval.Line M5 is inserted to connect the points z and a of line 91; line M6 isinserted to connect the points I) and c of line I66; line M1 is insertedso as to connect the points a: and y of line I12; line M8 is inserted soas to connect the points c and w of line 69; line 4I9 is inserted toconnect the points g and h of line 258; and line 426 is inserted toconnect points d and a" to connect shield grid I55 to cathode MI. Therest of the circuit in this embodiment operates as discussed with regardto the first embodiment above.

This invention is not limited to the particular details of constructionand processes described, as many equivalents will suggest themselves tothose skilled in the art. It is accordingly desired that the appendedclaims be given a broad interpretation commensurate with the scope ofthe invention within the art.

What is claimed is:

1. A timing system for use in supplying current through a load from avoltage source comprising means for controlling current from said sourcethrough said load, a pair of cascade connected controlled-ignitiongas-filled discharge devices, means responsive to current fiow in theleading one of said discharge devices for causing said controlling meansto conduct current through said load, means responsive to current flowin the other of said discharge devices for causing said controllingmeans to stop current fiow in said load, means for causing current tofiow in said one discharge device, time control means efiective onlyWhile said one discharge device is conductive for causing said otherdischarge device to conduct, and means for extinguishing said onedischarge device thereby extinguishing said other discharge device.

2. A timing system for use in supplying current through a load from avoltage source comprising means for controlling current from said sourcethrough said load, a pair of cascade connected controlled-ignitiongas-filled discharge devices, means responsive to currentfiow in theleading one of said discharge devices for causing said controlling meansto conduct current through said load, said responsive means including aninductive device in the path of said current flow, means responsive tocurrent flow in the other of said discharge devices for causing saidcontrolling means to stop current flow in said load, said last-mentionedresponsive means including an inductive device in the path of current ofsaid other discharge device and positioned to nullify the field of saidfirst-mentioned inductive device, means for causing current to flow insaid one discharge device, time control means efiective only whilesaidone discharge device is conductive for causing said other dischargedevice to conduct, and means for extinguishing said one discharge devicethereby extinguishing said other discharge device.

3. A timing system for use in supplying current through a load from avoltage source comprising means for controlling current from said sourcethrough said load, three cascade connected controlled-ignitiongas-filled discharge devices, means responsive to current fiow in thefirst of said discharge devices for causing said controlling means toconduct current through said load, means responsive to current flow inthe second of said discharge devices for causing said controlling meansto stop current flow in said load, means for causing current to fiow insaid first discharge device, time control means efiective 25 only whilesaid first dischargedeviceis conductive for-causing said .seconddischarge device to conduct, timecontrol means effective only while:said second discharge device is conductive for causing the third ofsaid discharge devices to conduct, and means responsive to current flowin said third discharge device for extinguishing said first dischargedevice thereby extinguishing said other discharge devices.

' 4. A timing system for use in supplying currentthrough a load from avoltage source comprising means for controlling current fromsaidsourcethrough said load, three cascade connected controlled-ignitiongas-filled discharge devices, means responsive to current flow in thefirst of said discharge devices for causing said controlling means toconduct current through said load, means responsive to current flow inthe second of said discharge devices for causing said controlling meanstostop current flow in said load, meansfor causing current to flow insaid first discharge device, time control means effective only whilesaid first discharge device is conductive for causing saidsecond-discharge device to conduct, and means responsive to-current flowin said third discharge device for opening the circuit of said firstdischarge device thereby extinguishing said-three discharge devices.

5. A timing system for use in supplying current through a load from avoltage source comprising means for controlling current from said sourcethrough said load, a pair of cascade con-- nected controlled-ignitiongas-filled discharge devices, means responsive to current flow in theleading one of said discharge devices for causing said controlling meansto conduct current through said load, means responsive to current flowin the other of said discharge devices for causing said controllingmeans to stop current flow in said load,means for causing current toflow in said one discharge device, a resistance capacitance circuitefiective only while said one discharge device is conductive for causingsaid other discharge device toconduct, and means for extinguishing saidone discharge device thereby extinguishing said other discharge device.v

6. A timing system for use in supplying current through a load from avoltage source comprising means for controlling current from said sourcethrough said load, three cascade connected controlled-ignitiongas-filled discharge devices, means responsive to current flow in thefirst of said discharge devices for causing said controlling means toconduct current throughsaid load, said responsive means including aninductive device in the path of said current flow, means responsive tocurrent fiow in the second of said discharge devices for causing saidcontrolling means tostop current flow in said load, said last-mentionedresponsive means including" an inductive device in the path of currentof said' other discharge device and. positioned to nullify the field ofsaid first-mentioned inductive device, means for causing current to fiowin said first discharge device, a resistance capacitance circuiteiiective only While said one discharge device is conductive for causingsaid other discharge device to conduct, a resistance capacitance circuiteifective only while said seconddischarge device is conductive forcausing the third of said discharge devices to conduct, and meansresponsive to current flow in said third discharge device for open-' ingthe circuit of said first discharge device thereby-extinguishingsaid'thr'ee discliargedevice's; I

7. -A timing system for use in supplyingcurrent through a load from avoltage source comprising means for controlling current from said sourcethrough said load, three cascade connected controlled-ignitiongas-filled discharge devices, means responsive to current flow in thefirst of said discharge devices for causing said controlling means toconduct current through said load, means responsive to current flow inthe second of said discharge devices for causing said controlling meansto stop current flow in said load, means for causing current to flow insaid first discharge device, time control means efiective only whilesaid first discharge device is conductive for causing said seconddischarge device to conduct, time control means effective "only whilesaid second discharge device is conductive for causing the third of saiddischarge devices to conduct, an impedance in the path between saidsecond and third discharge devices, and means responsive to voltage risein said path from ourrent flow in said thirddischarge device for openingthe circuit of said first discharge device vices.

8. A timing system for use in supplying current through a load from avoltage source com'- prising means for, controlling current from saidsource through said load, three controlled-ignition gas-filled dischargedevices, one of said devices having each of the other two of saiddevices in cascade arrangement therewith, means responsive to currentfiow in 'a 'second of said three devices for causing said controllingmeans to conduct current through said load, time con-' 'trol-meanseffective only while said one device is conductive for alternatelymaking said second device conductive and nonconductive, means forcausing said one device to conduct, time control means responsive tocurrent flow in said one device for causing said third device toconduct,

a resistance between said one device and said sponsive to current flowin said third device for extinguishing said first device therebyextinguishing said three devices.

9. In a timing system, three controlled-ignition gas-filled dischargedevices, one of said devices having each of the other two of saiddevices in cascade arrangement therewith, time control means efiectiveonly while said one device is conductive for alternately making a secondof said devices conductive and non-conductive, means for causing saidone device to conduct, time control means responsive to current flow insaid. one device for causing a third of said devices to conduct, aresistance between said one device and said other two devices in saidcascade arrangement for making said time control means for said seconddevice inefiective while said third deviceis conductive and said timecontrol means for Said third'device ineffective while said second deviceis conductive, and time control means for extinguishing said firstdevice thereby extinguishing said three devices.

10. In a timing system, a pair of cascade connected controlled-ignitiongas-filled discharge devices, a resistance in the path between saidleading one of said device's, time control means devices, means forcausing current to flow in the

